Consider the example of an MRAM device including a resistive cross point array of spin dependent tunneling (SDT) junctions, word lines extending along rows of the SDT junctions, and bit lines extending along columns of the SDT junctions. Each SDT junction is located at a cross point of a word line and a bit line. The magnetization of each SDT junction assumes one of two stable orientations at any given time. These two stable orientations, parallel and anti-parallel, represent logic values of ‘0’ and ‘1’. The magnetization orientation, in turn, affects the resistance of the SDT junction. Resistance of the SDT junction is a first value (R) if the magnetization orientation is parallel and a second value (R+ΔR) if the magnetization orientation is anti-parallel.
The magnetization orientation of the SDT junction and, therefore, its logic value may be read by sensing its resistance state. This is conventionally accomplished by sensing the resistance of the bit through the word and bit lines, which, in a resistive cross point array, act as write conductors during write operations, and sense lines during read operations. An alternate configuration utilizes a dedicated sense line in addition to the word and bit lines.
A write operation on a selected SDT junction is performed by supplying write currents to the word and bit lines crossing the selected SDT junction. The currents create two external magnetic fields that, when combined, switch the magnetization orientation of the selected SDT junction from parallel to anti-parallel or vice versa. However, too small a write current might not cause the selected SDT junction to change its magnetization orientation thereby resulting in the occurrence of half-select errors.
Conventional MRAM designs sometimes need two current driven magnetic fields to effectively switch the magnetization orientation and avoid half-select errors. However, the magnitude of the current(s) needed to switch the magnetization orientation of the SDT junction during a write operation should be as small as possible in order maintain the cost advantage of the implementation of the MRAM device.
Accordingly, what is needed is an MRAM device that reduces the current required to switch the magnetic orientation of the magnetic tunnel junction. The device and method should be simple, inexpensive and capable of being easily adapted to existing technology. The present invention addresses this need.